The project is a part of a general program investigating biochemical aspects of biosynthesis of neurophysins and neurohypophysical hormones, with a current emphasis on ectopic hormone-protein synthesis by tumors. The human tumor cell lines of small cell carcinoma of lung (SCCL) is a good model to study the relationship between tumor biology and ectopic peptide/protein biosynthesis. An attempt has been made to grow SCCL in vitro and screen them for the presence of neurohypophysial peptide hormones and neurophysins. Special attention will be focussed to elucidate the biochemical and immunological nature of vasopressin-neurophysin precursor(s). The understanding of ectopic hormone and protein biosynthesis by tumors may shed light on the nature of cellular differentiation and the process of malignant changes. Such a study also raises the possibility of presymptomatic detection of small cell carcinoma of lung and precise assessment of therapy.